The Nikon (new stock) cloth covered cables have low resistance and have a good, easy to use locking ring to hold the shutter open... Medium length would have lower resistance than a long one... Maybe you can make a little sleeve that fits under the plunger (over the cable) that acts like a handle on the cable so the cable end is easier to hold...
Then there is getting an old solenoid from a Speed Graphic lensboard, and wiring it to a little battery pack, and making a little link to the shutter release to fire it electrically...
Someone (not so many) years ago sold an adapter for cable releases that allowed it to be depressed with one's teeth...
Steve K
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